Clinical Tests of Lumbo-Pelvic-Hip Complex Function in Individuals with and without Scapular Dyskinesis: Implications for Identifying Individuals at Risk for Upper Extremity Injury

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Abstract

Scapular dyskinesis reflects suboptimal scapular function that may have damaging effects on surrounding structures. Due to its association with nearly all shoulder injuries, it has been recommended that the dynamic scapular dyskinesis test be performed during the clinical evaluation process of shoulder injury or pain. However, the shoulder complex relies on more than just the scapula for safe and efficient function. The ability of the shoulder complex to function efficiently depends greatly upon the lumbo- pelvic-hip complex to provide proximal stability for distal mobility, as well as to generate the forces and energy necessary to perform many upper extremity tasks. Therefore, previous research has also suggested the use of clinical tests of lumbo-pelvic-hip complex function to identify any proximal dysfunction that may decrease upper extremity function. Specifically, the single-leg squat has been proposed as an appropriate test of lumbo-pelvic-hip complex stability, due to its ability to reveal dysfunction at multiple segments of the kinetic chain in multiple planes of motion. While this recommendation has existed in the literature for quite some time, no authors have examined kinematics of the single-leg squat in individuals with upper extremity dysfunction. Therefore, the primary purpose of the current study was to examine trunk, pelvis, hip, and knee kinematics during a single-leg squat in individuals with and without scapular dyskinesis. Additionally, a single-leg drop landing test was used as a secondary test due to its more
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dynamic nature compared to the single-leg squat, which may be more revealing of lumbo-pelvic-hip complex dysfunction not evident in the prior test. Based on results from the scapular dyskinesis test, 32 participants were identified as having scapular dyskinesis, and 32 participants were healthy controls. The scapular dyskinesis test consisted of 5 repetitions of weighted shoulder flexion. Dyskinesis was considered present if there was excessive superior migration, inferior angle or medial border prominence, or dysrhythmia. After the scapular dyskinesis test, kinematics were collected while participants performed 3 repetitions of the single-leg squat and single-leg drop landing tests. Results indicated that trunk rotation, hip rotation, and knee valgus during the single- leg squat were significantly greater in the dyskinesis group compared to the control group. These findings may be valuable for clinicians during the shoulder evaluation process, as well as for the development of corrective exercise strategies for patients with shoulder injuries. There were some limitations to the current study. First, although scapular dyskinesis is associated with shoulder pain/injury, it is not considered an injury in and of itself. Therefore, the scapular dyskinesis group included participants with and without injury. Second, although previous research has highlighted some sex differences in single-leg squat and single-leg drop landing performance, both sexes were included in the current study in an attempt to generalize findings across sexes.